In the past, creation of detailed arrhythmia maps has required surgical exposure of the heart. Mapping of cardiac electrical activity by catheter is now possible, but is limited by the small number of electrodes which can be deployed and by difficulties in recording electrode locations. Thus, catheter-based arrhythmia therapies such as radiofrequency ablation have also been limited, with high success rates achieved for simple arrhythmias not reproducible for more complex arrhythmia circuits. The goal of the proposed project is to develop and validate catheter-based techniques for the creation of spatially accurate, high-density endocardial activation sequence maps which can be applied to clinical arrhythmias encountered in the cardiac catheterization laboratory. Using computer-assisted image and signal analyses, fluoroscopic and electrical data acquired during cardiac catheterization will be synthesized to allow clinical and research elecrophysiologists to map and to visualize stable arrhythmia circuits with a high degree of spatial resolution. The scattered positions of the mapped sites will approximate the geometry of the endocardial surface, and may be superimposed on fluoroscopic images of the heart to serve as a "roadmap" for catheter-directed therapies. To validate and extend this approach, the accuracy of this mapping technique will be tested against the electrophysiologic "gold standard" techniques, atrial morphometry and activation sequence determination using implanted electrode arrays, in an animal model of atrial arrhythmia. Additional studies are proposed to apply similar signal processing techniques to enhance the functional assessment of arrhythmia circuits using multielectrode catheters. In combination, application of these techniques will allow the functional anatomy of tachycardia circuits to be fully characterized and interpreted within the context of experimental arrhythmia research. The results of these investigations will be used to refine and apply this approach to the identification of specific arrhythmia mechanisms in human patients known to have similar, intractable atrial arrhythmias.